The present invention relates to a test head apparatus and process for a scanning probe microscope for the contactless testing of integrated electronic circuits.
In order to characterize and test integrated circuits on microchips, use is made nowadays of scanning probe microscopes, with the aid of which test tips for measuring the signal flows of the circuits are brought into the immediate vicinity of certain circuit elements. Today, such tips are produced by etching from a wire tail of the order of magnitude of xcexcm. The test heads an which the test tips are mounted can be positioned with an accuracy of just a few nm using modern scanning probe microscopes. Due to the coarseness of the available tips, however, it has hitherto not been possible to determine with sufficient accuracy either the precise location of the tip or the distance between tip and probe. An additional measuring effort is required to position the tip and to pull it back in a defined manner so as to prevent damage.
In order to measure the desired parameters of an integrated circuit, the test head is moved by microscope control to a specified position and the measurement is performed. If several different variables are to be measured, it has so far been necessary, after each measurement, to move a probe suitable for the next variable to be measured to the test position before that variable can be measured.
As a consequence of advances in the miniaturization of circuits, the dimensions of the conductors and components of the circuits as well as the intensity of the signals carried in the circuits during operation are becoming smaller and smaller. Furthermore, the frequency at which modem microprocessors are operated is constantly rising. In the meantime, it has become necessary to perform signal measurements on circuit components of dimensions of the order of magnitude of 100 nm at frequencies of the order of magnitude of 1 THz. The capacitance of present-day capacitive measuring probes is too high for the measurement of super high frequency,signals. The presently available magnetic field-sensitive probes used for measuring magnetic fields which are employed to determine the currents in the circuits cannot yet be produced either with the requisite fineness.
An object of the present invention is to provide a test head apparatus and process for a scanning probe microscope for the accurate and rapid testing of a modem LSI circuit. The measurement of. several different variables at a test location is thereby to be possible without moving the test head. The test head is to be producible simply and at relatively low cost using existing tools.
According to the present invention a group of probes produced by three-dimensional additive lithography, having at least one electrically insulating, tapered-ending body as scanning force probe for scanning the topography of the circuit, having at least one capacitive probe for measuring signal pulses and having at least one magnetic field-sensitive probe for measuring electric currents, as well as having at least one tapered conducting body as field emission probe is disposed on a substrate, in that the probes are directed at a point situated centrally above the group of probes, and in that the conducting probes as well as the base end of the capacitive probe are joined to conductor structures on the substrate for connection to a test circuit. In this context, it may be provided that the scanning force probe projects above the other probes.
As a result of the orientation of the probes around a central point, the sensitivity of the probes is greatest in that direction. The test head is moved to a measuring point by means of the slightly projecting scanning force probe. The signals of the integrated circuit available at that point can then be measured simultaneously by various probes, without the necessity of moving the test head.
In experiments, it has proved advantageous if the probe bodies have maximum diameter of the order of magnitude of 100 nm head.
By means of techniques of three-dimensional additive lithography, bars and conductive tips can be disposed on a substrate at any angle of inclination with a placement accuracy of 5 nm. Furthermore, electron beam-induced deposition, in particular, permits the production of arches, disks having openings or the like with the same accuracy.
In electron beam-induced deposition, the vapor of specific substances is directed onto a substrate surface, where it is atomized by a fine electron beam. Thereupon, the atoms combine with the aid of further electrons to form a solid consisting of minute crystallites. By appropriate control of the beam, it is thus possible to produce structures of virtually any form. It is possible to make the structures from different materials. Thus, for example, it is also possible to produce electrically conductive wires surrounded by an insulating jacket or externally reflecting light-conducting structures of extremely small dimensions.
The probes according to the invention required for the testing of an integrated circuit can, using the aforementioned technique, be arranged with great accuracy on a surface measuring just a few square micrometersxe2x80x94it being possible for said surface to be disposed on a conventional cantileverxe2x80x94and can be oriented towards a common measuring point. The resolutions in respect of location required for the testing also of LSI circuits are obtained using probes according to the invention.
In order to simplify signal evaluation and resolution with respect to time, it is provided that an amplifier circuit having electric amplifier tubes for amplifying the test signals supplied by the probes, the electric amplifier tubes being executed in three-dimensional nanolithography in the immediate vicinity of the probes, is disposed on the substrate.
Further subclaims contain advantageous embodiments of the substrate as well as of the individual probes. Such probes can be produced by techniques of three-dimensional lithography.
To adjust the test head over a measuring point, it is provided that the scanning force probe is guided contactlessly over the integrated circuit to the intended measuring site and that, when above the measuring site, the scanning force probe is moved towards the integrated circuit until the force acting between the scanning force probe and the integrated circuit reaches a given value.
In the search for defective locations on an integrated circuit, printed circuit traces of the circuit are, inter alia, provided with a charge which is picked off again after a certain time. If the charge has changed in the meantime, this indicates a defective location on the integrated circuit. For subjecting a printed circuit trace of an integrated circuit to an electric charge using a field emission probe according to the present invention, it is provided that the field emission probe is operated in moist air or is coated with a water-containing film and that the field emission probe is moved towards the printed circuit trace of the integrated circuit which is to be charged and, by applying a voltage to the field emission probe, OHxe2x88x92 ions are separated out of the film and pass over to the printed circuit trace, with the result that the printed circuit trace is negatively electrically charged.
Through the use of ionized water molecules, it is possible to select the polarity with which the printed circuit trace is charged. In order to be able to charge a plurality of printed circuit traces simultaneously without there being any mutual interference which might falsify the measurement result, it is provided that, after a printed circuit trace has been charged with a negative charge, the field emission probe is moved to a next printed circuit trace and a reverse voltage is applied to said field emission probe, as a result of which the printed circuit trace is positively electrically charged by H3Oxe2x88x92 ions separated out of the film, and so forth, with the result that adjacent printed circuit traces are charged with different polarities.
In order to obtain information about the composition of the printed circuit traces of the circuit under test, it is provided in a further refinement of the present invention that the scanning force probe comprises an SNOM (Scanning Near-field Optical Microscope), that light is emitted from the SNOM tip and that, along with the light, photoelectrons are released from the material of an adjacent printed circuit trace, with the result that, by spectroscopy of the escaping radiation, the material of the printed circuit trace can be deduced. Such a probe tip can likewise be produced in its entirety using an epitaxial growth method.